Related parameters of a Radio Link Control (RLC) timer at an acknowledged mode in a Long Term Evolution (LTE) system are basic protocol-defined parameters. These parameters are necessary parameters of an LTE infrastructure network. Whether these parameters are properly configured and can better adapt to a traffic status in the network directly affects network resource occupation and user experience.
Theoretically, Length of a polling retransmission timer=Air interface transmission delay of a protocol data unit (PDU) that carries a polling identifier bit+Scheduling delay of a peer end status report+Air interface transmission delay of a status report; and
Length of a status report prohibit timer=Air interface transmission delay of a status report+Scheduling delay of peer end retransmission data+Air interface transmission delay of retransmission data.
The air interface transmission delays in the foregoing formulas may be considered as fixed duration, and length configurations of the two timers are strongly related to the scheduling delay of a status report or the scheduling delay of retransmission data. In a network, a scheduling delay is related to a quantity of users. If the quantity of users is relatively large (large traffic scenario), and a quantity of users for scheduling increases, a time interval at which each user obtains a scheduling opportunity becomes longer. Therefore, the scheduling delay of a status report or retransmission data also becomes longer.
If a configuration value of the polling retransmission timer is smaller than a peer end scheduling interval, before a peer end status report is fed back by obtaining a scheduling opportunity, the polling retransmission timer times out, and this triggers unnecessary retransmission. Moreover, an increase of retransmission times increases a probability of RLC maximum retransmission times, and this causes a call drop. If a configuration value of the status report prohibit timer is smaller the peer end scheduling interval, before peer end retransmission data is fed back by obtaining a scheduling opportunity, the status report prohibit timer times out, and the status report is sent again to the peer end. This wastes resources and may cause the peer end to send retransmission data for a second time.
Downlink data sending is used as an example, that is, an evolved NodeB (eNodeB) sends data to user equipment (UE). A condition when the polling retransmission timer is configured improperly is described as follows:
The eNodeB sends downlink PDU data that carries a polling identifier bit to the UE, and enables the polling retransmission timer at the same time;
the UE receives the downlink PDU data that carries the polling identifier bit and that comes from the eNodeB, and waits for an uplink scheduling opportunity to send a status report to the eNodeB; and
a time for which the UE waits for the uplink scheduling opportunity exceeds a length of the polling retransmission timer on an eNodeB side. As a result, the polling retransmission timer on the eNodeB side times out and still does not receive the status report from the UE. Therefore, the eNodeB considers that the UE does not receive the downlink PDU data, and retransmits, to the UE, the downlink PDU data that carries the polling identifier bit. The retransmission in this case is considered as invalid retransmission.
In the prior art, unnecessary RLC retransmission and RLC status report sending are caused, and this wastes radio resources. In addition, an increase of retransmission times increases a risk of reaching RLC maximum retransmission times and causing a UE call drop.